This invention relates to a process for separating suspended solids from the tailings fraction of phosphate ore.
Phosphate ore contains substantial amounts of impurities, largely clay and sand. In the usual treatment of the ore, the ore is first broken apart into small pieces and then separated into a concentrate and a waste or tailing. The tailing fraction contains extremely fine clay and sand particles. Because of their minute size, the particles, when carried in water, remain suspended in the water for relatively long periods of time. Such suspensions of tailings are known as slimes.
Disposal of the slimes of phosphate tailings presents a problem. At present, the slimes are discharged into large settling ponds where the extremely fine suspended solids eventually settle to the bottom of the pond. The process is slow and transforms large areas of potentially valuable lands into unsightly and dangerous lagoons. Obviously the problem of disposal would be greatly reduced if the slimes could be concentrated into a relatively dense sludge quickly and efficiently. Government regulations which require that phosphate waste tailings be returned to the open pit mines for reclamation of the land provide another impetus for a quick and efficient method of producing a relatively dense sludge. One means for preparing a dense sludge is through the use of mechanical thickeners.
In U.S. Pat. No. 3,622,087 a process is described for producing a relatively dense sludge of sand and clay from phosphate tailings through the use of thickeners. However, the process is complex and requires several thickening stages in order to produce a satisfactory sludge. For example, the solids concentration of the sludge is 5 to 6 percent after a first thickening, 12 to 14 percent after a second thickening, and about 22 percent following a third thickening stage. There remains a need for a method which produces a thickened sludge more efficiently.